The present invention relates to a sound isolation plate, for example, an under cover provided on the bottom of the engine room to reduce the noise on the outside of the car, which is capable of meeting compatibility between a sound isolation property to reduce noises and an air permeability to radiate heat from the engine room.
As shown in FIG. 1, the under cover 3 is fitted on the bottom of the engine room 2 of the common car 1. This under cover 3 prevents an oil pan of the engine, etc. from directly striking against protruded things on the road. Also, the under cover 3 functions as a sound isolation wall to suppress an engine noise which is radiated from the engine room 2 to the outside of the car.
A fitting area of the under cover 3 wider, a sound isolation effect achieved by the under cover 3 higher. However, if the fitting area of the under cover 3 is increased, a sealing degree of the engine room 2 is enhanced by such under cover 3 and thus the air permeability of the engine room 2 is lowered. It is likely that an increase in an atmospheric temperature of the engine room 2 is caused. Therefore, in practice the air permeability must be assured on a preferential basis. As a result, a limitation is imposed on an improvement in the sound isolation effect by virtue of an increase of the fitting area of the under cover 3.